The invention relates to a vibration motor.
Vibration motors of this type are known by various names, such as traveling wave ultrasonic motors, vibration wave motors, and ultrasonic or piezoelectric motors. Exemplary embodiments of such vibration motors are found for instance in U.S. Pat. Nos. 4,771,203; 4,739,212; and 4,755,705; and in the article by Prof. Dr. C. Reuber entitled "Piezo-Wanderwellen-Motor" [Piezoelectric Traveling Wave Motors], Elektronik Journal [Electronics Journal] 23/89, pp. 43 and 44.
In such a vibration motor, the stator is set to vibrating by the piezo excitation system, in the manner of a rotating mechanical traveling wave. By means of the pressure-exerting element, typically embodied as a cup spring, a slipfree connection between the motor and the stator is established, with which the force is transmitted to the rotor, causing it to rotate.
In the currentless state of the motor, the pressure exerted between the rotor and stator for the sake of a slipfree connection blocks the driven shaft, which is connected to the rotor in a manner fixed against relative rotation. Accordingly, a motor of this type cannot be used for applications that require rotation of the driven shaft in the currentless state of the motor. One example of such an application is a throttle valve adjuster in internal combustion engines, in which for safety reasons a restoring spring assures that the throttle valve is always returned to the closing position if the throttle valve adjuster is without current.